For those just starting out in airsoft, few topics can be more intimidating to broach than HPA.
Sometimes it feels like the slightest mention of building or buying an HPA gun can cause more experienced airsofters to explode into heated and often passionate debate over their actual benefits and uses, with various esoteric terms and numbers being hurled around.
But HPA airsoft guns, and their component parts, don’t have to be confusing or really all that complicated to understand.
They are fairly straightforward and they still offer some significant advantages and disadvantages that airsofters should be aware of before making any decision.
If you feel you might be interested in exploring the world of compressed air, or just want to broaden your overall airsoft knowledge a bit more, then read on as we discuss HPA in airsoft.
What Does HPA Stand For In Airsoft?
In airsoft, HPA stands for High-Pressure Air, a way of powering an airsoft gun using an external tank of pressurized air, rather than an internal gas tank or external cartridge filled with green gas or CO2 (as is common with gas blowback airsoft guns), or a gearbox that compresses air inside the gun, such as in an AEG.
How Does An HPA Airsoft Gun Work?
HPA airsoft guns are pneumatic devices, that is they work through a controlled release of compressed air.
There are different HPA systems out there, for sure, but the essential concept is pretty similar across them all.
The way HPA works is that an airsoft gun is connected to a tank or bottle filled with highly pressurized air (3000 PSI or 4500 PSI/206 or 310 BAR).
These tanks have a built-in output pressure of about 300-800 PSI (thanks to what’s called a bottle regulator), which is still far too much for most HPA systems and airsoft guns, and not something you want launching BBs at friends and strangers.
HPA tanks are therefore connected to an external regulator, which brings the PSI down to a lower, more manageable level (usually to a maximum of 130 PSI at most) and keeps the flow of air consistent and available.
The regulator connects to a hose, which carries the stepped-down pressurized air down a line, a kind of air hose, that is anywhere from 24” (50cm) to 46” (116cm) or even longer and into the gun and its engine.
With each pull of the trigger, a blast of pressurized air is released and propels a BB through the hop up unit and out the barrel towards a target.
When a tank finally runs out of air, users take them to a refill station that has specialized air compressor equipment and experienced staff to do so safely.
These can be found in some airsoft fields, most paintball stores and even dive shops.
Required HPA Equipment
The HPA tank is where it all begins.
Like a paintball air tank or even a basic SCUBA tank, an HPA tank is filled with compressed air, typically held at 3000 and 4500 PSI.
Now those numbers might pop out at you as being pretty high pressure for airsoft (or paintball), and you’d be right.
HPA tanks don’t simply release air at 3-4500 PSI, but rather have a bottle/cylinder regulator attached to them that bring the PSI down to a more manageable level, typically between 300 at the low end (Super Low Pressure/SLP tanks) to 950 PSI, with most outputting at 850 PSI.
Since 850 PSI is still very, very powerful for airsoft, most HPA kits use a second stage regulator, which we discuss below, in order not to blow the engine.
One thing to note is that good quality bottle regulators tend to have what’s called a burst disk installed, which is a safety feature that vents the tank in case it is accidentally overfilled, preventing the tank itself from blowing.
HPA tanks come in different sizes, measured in cubic inches (CI), from small 13 CI tanks to giant 100+ CI tanks.
As you can imagine, the larger the HPA tank, the more compressed air it can hold at a certain pressure and the more shots you can get out of it.
On the flipside, the bigger the tank, the heavier and more bulky your rig is going to be.
How many shots you get out of a tank can be quite variable.
It depends a great deal on the PSI you’re running through the regulator, the tank’s pressure (3000 or 4500), the tank’s size and a rig’s overall efficiency.
The bigger the tank, the more pressure it’s held under and the lower the regulator PSI (or FPS) the more shots you’ll get out of it.
That said, you can usually get around 1000 shots or so from a 13/3000 (13 CI @ 3000 PSI) running at 100 PSI and 3-4000 from a decent, 68 CI 4500 PSI tank running at 100 PSI.
HPA Tank Types
HPA tanks are made of a couple different materials, each with different properties.
HPA tanks made of aluminum tend to be quite a bit cheaper to buy than carbon fiber tanks, but also tend to be heavier.
They come pressurized at 3000 PSI, so hold a smaller volume of air pound for pound (50% less air than an equally sized carbon fiber tank), so tend to offer fewer shots before needing a refill.
HPA tanks made of carbon fiber are a lot more expensive than similarly-sized aluminum ones, which can be an issue for some players, but do hold a lot more air and are a lot lighter to carry around than aluminum, so are a lot easier to use in a game (fewer refills/less sweat equity).
For those that can afford them, carbon fiber HPA tanks tend to be the preferred option.
With a tank outputting 850 PSI, and a typical HPA engine only being able to take an operational pressure of about 100 PSI, obviously there is a step missing here.
That step is a secondary regulator.
These regulators usually attach to the top of the HPA tank and bring the outputted air pressure down to a far more reasonable 50-180-ish PSI…i.e, something that can be used without causing your HPA engine to self-destruct.
They also act to keep the flow of air constant so that the engine doesn’t suddenly face a lack of air pressure.
Regulators either come with or can be fitted with a Quick Disconnect (QD) Fitting. These come in different sizes (4mm/6mm) to fit different hose diameters and basically lets you attach and detach lines from your rig without releasing air from the tank.
HPA lines or hoses run from the regulator to the gun.
These come in an assortment of lengths (24”/50cm to 46”/116cm) typically) and diameters (3mm to 6mm) and generally are rated to accommodate a certain amount of pressure before being damaged.
In terms of length, it’s important to find a good balance between being long enough to handle and move an HPA gun around comfortably, and being too long that the line snags or gets tangled up.
Most players should do fine with a 36”/91cm line but it really depends on a person’s height, arm span and personal taste.
In terms of construction, there are a few different HPA line types out there.
At their simplest, HPA lines can be a simple, easy to find and cheap cut of rubber tubing that’s rated for high pressure air.
Others, such as the Amped line, have a woven, usually nylon, exterior. These are more expensive but also more durable and resistant to tearing and damage.
The HPA engine is the heart of an HPA build.
The HPA Engine essentially converts the rush of pressurized air into something that will consistently fire a 6mm BB through an inner barrel with a squeeze of a trigger.
HPA engines can be built in many different ways, with many different models and generations of models out there to choose from, but the basics tend to remain the same.
A valve allows a certain quantity of compressed air in, passing through the system and then to the nozzle.
The nozzle, as with other airsoft guns, passes the air flow from the cylinder chamber through the hop up and out the inner barrel.
One thing to note when dropping an HPA engine into a pre-existing gun is that nozzles can be fairly specific to certain models of airsoft guns, a nozzle might be designed to fit a Classic Army AUG for example.
Like airsoft AEG gearboxes, HPA Engines can be fitted (and many come with) a fire control unit (FCU).
Like a Mosfet/ETU setup, these connect to and basically electronically control the HPA engine and can provide a lot of different settings for users to play around, depending on the unit in question obviously, with such as:
- Dwell – poppet dwell, holds the solenoid open and controls the volume of air flow in a barrel. Can be optimized for different barrel lengths.
- Fire modes- providing an HPA rig with settings for multiple-round burst mode and automatic fire
- Closed Bolt mode – the nozzle is pressed forward and keeps a BB loaded between trigger pulls.
- Open Bolt mode- the nozzle is held back, loading and firing a fresh BB with every trigger pull.
- Rate of Fire adjustment – adjust how many BBs per second the engine will put out on automatic and burst mode
- And more
Pros And Cons Of HPA Guns In Airsoft
Can get very high FPS out of these very easily
HPA rigs are capable of very high PSI. As long as the gun itself can handle it, you can usually get a much higher FPS than other options out there, increasing the range and accuracy of the BBs you fire (all else being equal).
Tunable FPS makes airsoft guns very versatile
Part of the attraction of an HPA airsoft gun or rig is the ability to adjust the regulator up or down, adjusting PSI (and, ultimately, FPS) up or down with a very fine degree of control.
Users can take the same gun to an outdoor event, set it up to fire 450 FPS, and then head to an CQB game with the same gun and quickly tune it down to chrono at 300-350 FPS.
Adding to the versatility of an HPA rig, they are usually outfitted with fire control units (FCUs) that can allow for even greater control, offering users helpful functions such as fire modes and customizable RPS.
While it’s true that many higher-end AEGs offer limited FPS tuning via spring adjustment, such as with the KWA Ronin T6s , they can’t really provide the same range and fine degree of control that a regulated tank can offer.
Reliable and require less maintenance
The simple fact is that HPA guns have fewer internal parts compared to AEGs, i.e. there is less inside that can go wrong.
Most good quality HPA engines are built to pretty high tolerances and are relatively simple, mechanically speaking, while regulators are generally built to specific standards and will generally last some years if used properly.
Compare this to the intricate, often questionably built, system of gears and related parts inside an AEG gearbox, or even a system of tiny nozzles, valves and pistons of a GBB pistol, and the difference can be night and day.
Maintenance, too, is quite a bit simpler with HPAs.
A properly put together rig mainly requires users to lube and change o-rings every so often (every 10 000 round so so), as well as to re-hydro their tanks every few years, which means bringing them in to a paintball store or dive shop and having the tanks visually inspected and filled with pressurized water to look for any leaks.
Can have superb trigger response
Trigger response on HPAs tend to be extremely quick and responsive, partially due to the more simplified internals and constant flow of air.
And with advanced FCUs and aftermarket speed triggers, they can be easily set up with a hair-trigger providing users with almost real steel firearm responsiveness.
Compared to real steel guns, airsoft guns are pretty quiet in general.
HPA airsoft guns take things a step further.
While AEGs can be somewhat quiet the sound of their pistons, gears, cylinders and whirring motors working in unison can be fairly noticeable when they’re fired.
Similarly, gas airsoft guns are often favored because of the somewhat loud and noticeable noise and action they produce.
Because of their more constant air pressure and few moving parts, HPA rigs tend to be very quiet, with their noise mainly being limited to a quiet pop of air when fired…something that can actually be silenced even further with a mock suppressor, as demonstrated in the video below.
As such, HPA rigs let users really stalk around an airsoft field unnoticed, making them a great option for ambushing opponents or for sniping.
If you are someone who collects airsoft guns and have multiple HPA airsoft guns, you can often use the same tank system on different guns, letting you swap between guns as needed while keeping costs down.
More Consistent FPS
Whether controlled by a circuit board and valve or just by a simple pressure valve, HPA guns have a very consistent FPS.
For safety reasons, compressed air valves are very well built and precise and so the amount of air pressure flowing through tends to remain the same. Ultimately, this means that users will only see about a +/- 1-3 FPS during shooting, which is markedly more consistent than the +/- 20 or so FPS that many AEGs or gas guns can be susceptible to.
Further, running on compressed air means they offer more consistency in cold weather compared to CO2 and even green gas guns, suffering far less of a drop in performance when the temperature dips, although obviously you still have to worry about o-rings and internal buckings freezing and cracking in extreme weather.
Upfront cost can be high
With AEGs and gas airsoft guns, your initial cost can be pretty low.
Usually you can get away with buying the gun, some ammo and some of whatever powers it, whether that is a battery or some gas cartridges.
With a typical HPA rig, on the other hand, you’ll also need to buy the gun, ammunition, a tank, a regulator that meets the output of that tank, a line and (if you’re converting an AEG) some kind of HPA engine.
While most of those will be more or less one time costs, the initial outlay of money can be higher than an AEG or a gas airsoft gun.
Lack of realism
Many players get into airsoft due to the realism of airsoft guns.
The ability to handle and use something that, for all intents and purposes, looks just like a real life firearm can be a big draw, particularly if that replica is based on a restricted firearm of some kind.
Compared to AEGs and GBB airsoft guns, HPA airsoft guns aren’t exactly the most realistic simulation of a real steel firearm.
With their tanks and hoses and regulators, they look more like a flamethrower than a firearm.
Further, they make very little noise and have no real simulated recoil, and you don’t have the same freedom of movement as you might with a disconnected airsoft gun.
All this means that when using an HPA airsoft gun you will probably be very conscious that you are using an HPA rig, which means your game play will ultimately be a little less immersive.
They’re Bulky and Heavy
HPA airsoft guns tend to require the use of an air tank and regulator, which will be strapped onto your body somehow and which you will need to carry around for the duration of your game.
These tanks and regulators are somewhat bulky in size and they can weigh anywhere from 1.5-5 lbs depending on their dimensions and construction.
Although not the heaviest thing in the world, it does mean you will be carrying more weight on you than an AEG or GBBR player.
Lines can be annoying
For the most part if you’re using an HPA airsoft gun, you’ll probably have a line or hose swinging from your gun.
These lines can be annoying and can get tangled, caught up or otherwise just get in the way during a game, especially if you’re playing outdoors in woody areas or in tight, CQB fields.
They have also been known to kink, which can drop the power output of your gun quite noticeably.
Not every airsoft field allows them or may restrict them
Due to past player misbehavior, complaints and even injuries, some fields have banned players from using HPA airsoft guns.
Other fields place restrictions on HPA guns, often requiring users to lock their regulators (to prevent users from cheating their chronos by surreptitiously turning up the PSI when the ref isn’t looking) by using either zip ties or making users purchase tournament locks.
While this isn’t true of all fields, and may not matter if you have your choice of airsoft fields around, it can be an issue if you live where there is a noticeable lack of field options.
Refilling them can be a bit tricky, depending on where you live
Unlike an AEG or a GBB airsoft gun, refilling an HPA tank isn’t as simple as plugging in a charger or swapping a cartridge.
Because of the high pressures involved, refilling a tank safely and competently requires some professional expertise and some professional equipment.
This means that if you run out of air in game, you’ll have to stop and take your tank to a refilling station (if the field has one) and perhaps even forking out a couple bucks per 1000 PSI.
Using HPA tanks also means that every few years you’ll have to get your tanks tested and certified as safe and leak-free in order to prevent catastrophic and potentially dangerous equipment failure.
Tankless Airsoft HPAs?
Many potential HPA rig owners are put off by the idea of having to deal with pressurized air tanks and lines (maintaining them, carrying them around, etc).
Such users might be interested to know that there are a few tankless airsoft HPA rigs and guns out there.
These usually involve directly hooking the engine up to a CO2 cartridge that is located somewhere inside the gun (usually in the buffer tube).
On the plus side, tankless HPAs mean that users don’t need to fiddle with or carry HPA tanks and deal with lines, which can make the overall experience a little more realistic and a little less cumbersome for users.
On the downside, tankless HPAs become a bit more like a gas airsoft gun.
By using CO2 cartridges, users lose out on some of the consistency that a direct connection to a pressurized tank provides and users can’t simply hook their guns up to a larger tank to get more shots if they so choose.
There are also fewer ready tankless HPA models out there to choose from and they can be quite a bit more expensive than a standard rig.
Are HPA Airsoft Guns Really Worth It?
Whether an HPA airsoft gun or rig is worth its cost really depends on the person.
With fewer moving internal parts to worry about, they are considerably easier to maintain than most AEGs out there.
They also provide excellent FPS consistency, exceptional trigger response, and are highly configurable and customizable.
Similarly, HPA rigs are able to power down or up extremely easily as the situation may demand and without any need for dealing with springs or programmable mosfets.
If you’re someone who likes to take your guns to different types of games, such as outdoor, indoor, speedsoft and CQB, it might be a better choice.
They are also exceptionally quiet compared to other airsoft gun types out there, making them ideal for users who prefer an ambush style of play.
That said, HPA rigs and all their equipment can require a considerable upfront investment (and cover ongoing certification costs), and you will have to carry all the equipment around in game.
Another thing to consider is where you live.
Some fields restrict or even ban the use of HPAs, and even if they are allowed the local airsoft community may frown upon them due to negative past experiences with HPA players.
Having a really fancy HPA rig may not be of much use if you can’t use it properly (or at all) or if nobody wants to face you on the field.
Comparing Airsoft AEGs Vs HPAs
When considering an HPA rig, most airsoft players will probably ask themselves – well, why don’t I just buy an AEG and call it a day.
And it is a pretty legitimate question.
AEGs and HPAs both allow for relatively quick fire, can be customized to a fair extent, can be fitted with programmable controllers and offer lots of settings to play around with.
That said, when you compare the two, they do have their own relative advantages and disadvantages that potential buyers need to consider before making a purchase.
HPAs compared to AEGs
|Faster trigger response, lighter pull||More expensive|
|Quieter||May need to pay for refilling tanks, periodic inspections|
|Some units don’t need batteries at all||Have to carry around all the equipment on the field|
|Fewer internal parts that can break||Not as realistic to handle|
|Tanks can last multiple games|
|Greater out of the box FPS consistency|
|Easier to finely adjust FPS manually|
AEGs compared to HPAs
|No need for any tanks, hoses or regulators||Noisier|
|A lot more upgrade parts and customization options available||Gearboxes, motors and internals will wear out and break faster|
|A lot cheaper to buy and run||Requires batteries|
|Every field allows AEGs in as long as they meet FPS requirements||Needs several customized parts to get a similar trigger response and ROF|
|High quality AEGs can be super accurate and fairly consistent|
|Better AEGs let you adjust FPS either through programmable Mosfet/ECU or via spring adjustment|
|Lighter to carry|
|More ready options out there|
What Kind Of Airsoft Guns Can Be Fitted With An HPA System?
HPA engines can, and have been, fitted to most kinds of airsoft guns out there.
If you play long enough and go to enough fields, you are sure to see HPA pistols, rifles, SMGs, machine guns, DMRs, sniper rifles and even shotguns.
Can I Convert An AEG Airsoft Gun To An HPA Rig?
If you have a favorite AEG and you want to convert it to HPA, it is possible using an HPA engine.
A number of companies make drop-in models, which are designed to take the place of the gearbox internals in an AEG gun.
These drop-in HPA engines generally include the HPA module, programmable/adjustable FCU, selector plate and trigger module and so, after running the line, are pretty much ready to go and aren’t really that much of a headache to install.
These units are designed to run off an AEG’s existing LiPo battery and are generally as easy as it gets to install so long as you find one that fits the particular AEG gearbox in question (V2, V3 and so on).
Can I Convert A GBB Airsoft Gun To An HPA?
You can convert a GBB airsoft gun to be able to run HPA. How easy this is really depends on the method you choose to do it.
There are a couple body kits out there for some airsoft gun models that can help convert a GBB/GBBR’s internals to an HPA rig, but these can get very tricky and tend to be very expensive (> $500 in some cases).
Usually, a better option is to tap a gas airsoft gun’s mags.
This is where a gas airsoft gun’s magazines are fitted with an HPA tap that allows users to run a line directly into them, leaving the internals of the airsoft gun more or less alone.
Those that don’t like doing so can find aftermarket adaptors in most cases and there are even ready HPA mags for some airsoft models.
The trick really then becomes making sure that you run PSI that won’t damage the airsoft gun in question (a green gas airsoft gun can take far less PSI than a CO2 one before breaking).
On the downside, of course, this means that you probably will have to disconnect and reconnect lines after every mag change.
Running HPA in airsoft can be a great option for the right player.
With their increased consistency, reliability, customizability and versatility, HPA rigs have distinct advantages over their AEG and GBB rivals.
That said, with their greater up front cost and somewhat cumbersome nature, they may not be to every player’s taste and so careful consideration must be made before making a decision.
Will Martin – Will has been into airsoft and paintball for well over 10 years, and has done it all – from upgrading and fixing gearboxes as a tech to building custom airsoft loadouts for his friends to supporting off those friends as a DM.
Ted Clark– Hailing from Florida, Ted has been an avid airsoft enthusiast since he was in middle school. When he’s not checking out and reviewing airsoft guns, he enjoys picking off his enemies one by one on the field as a sniper.